PROVIDENCE, R.I. — Authorities are trying to determine what caused a support frame to collapse during an aerial hair-hanging stunt during a circus performance, sending eight acrobats crashing to the ground and onto a dancer below. At least three remained in critical condition Monday morning, hospital officials said. The accident occurred Sunday during the Ringling Bros. and Barnum and Bailey "Legends" show during an act in which the circus says eight performers hang "like a human chandelier" using their hair.